Evidence is presented that mice are well-suited for stress, aging and drug studies in a social context. However, there is need for laboratory methods of evaluating patterns of social response in freely breeding colonies where males and females, old and young, and dominants and subordinates can interact under approximately natural conditions. This project will advance the development of a measurement system designed to do this. The present device uses a complex population cage divided into areas for nesting, eating, drinking, and exercise. Permanent magnets implanted under the skin of the back or belly of the mice trigger electronic check points at the entrances to each of these areas. The implanted animals are thus monitored as they move through the various parts of the system. The detectors generate signals which are digitally encoded by logic circuits identifying each mouse according to the orientation and position of the magnets. The digital information is handled by a minicomputer and transactions of four separate animals are displayed and evaluated. At intervals, the number of passages and elapsed time spent in each of the eight areas are tabulated. These measures are reported for each movement as it occurs, thus permitting study of social interactions. The present project plans to move from this experimental prototype to a user oriented and more readily maintained and serviced system which is made up of modules to facilitate trouble shooting. The caging will be interlocked so that it is easier to assemble. Improved methods of magnetically tagging the animals will be examined. In addition, a new speeded up system that detects each magnet's pole as it passes the portal will be employed. It will track eight instead of only four animals and add measures of velocity of passage through a portal, hesitancy and chases to the entry-exits and elapsed time in the area determined by the original device. It will also identify which animals have displaced magnets which are not triggering effectively. The new system will be employed in conjunction with visual observations of test colonies to evaluate its accuracy and determine the most effective techniques of data analysis in terms of social interaction.